The present invention relates to a sample injection device, particularly to require only one external control solenoid valve to activate three micro valves in corresponding application of gas chromatography. Therefore, this invention can be employed a much less pressure process with sample injector.
In general, gas chromatograph is the most widely used instrument for analysis of gas mixtures. A gas chromatograph include three major components: an analytical column which physically separates the components of the mixture, a detector which senses the individual component after separation, and an injector which introduces a fix amount of gas sample and carried to analytical column by carrier gas. The most conventional injection techniques are syringe and sample loop methods. The later includes a six-port rotary valve, in which the sample is first introduced into the loop while a carrier gas flows to the analytical column through channels in this device. When the rotor is turned into a proper position, usually one-sixth of a turn, the sample loop becomes part of the channel that conducts the carrier gas into the analytical column. Therefore, the sample is swept into the analytical column. In the recent decades, portable micro gas chromatograph has attracted much attention. A palm-size gas chromatograph has become a reality in recent years due to advances in lab-on-a-chip. This six-port rotary valve injector is slow in response, and very difficult to fabricate into a miniature fixture for micro gas chromatograph. In addition, the rotary valve wears out easily. Apparently, it is not suitable for micro gas chromatograph.
There have been several designs for micro-machined injector In existence. They usually contain several micro valves each connected to a solenoid valves for control, separately. U.S. Pat. No. 5,487,313, entitles xe2x80x9cFluid-lock fixed volume injectorxe2x80x9d issued on Jan. 30, 1996, and incorporated by references herein, describes a sample injection scheme which requires pressurization and storage of the gas sample in a chamber up to 80 psi, and then inject a fixed amount of sample by time opening the micro valve. Four valves confine the pressurized gas In the sample chamber. By so doing, the micro valves must be capable of withstanding such a high pressure without leaking. It requires many precisely controlled silicon micro fabrication steps. Besides, all these valves are activated by external controls independently.
To simplify these problems, we developed a novel design of sample injector, which requires only one external control solenoid valve to activate three micro valves in the injection system and much less pressure.
Due to the continuous development of chemical industry, requirement of instrument for analysis of gas mixtures is always important. Thus, the improvement of sample injection device is to be of great urgency.
Therefore, the main object of the present invention is to provide an external control solenoid valve to activate three micro valves in the injection system.
Another object of the present Invention is to reduce the production cost for a sample injection device.
Specifically, the present invention of a sample injection device for micro gas chromatograph is assembled from five layers of thin plates and membrane. The first layer serves as cover plate and interfacial connection to outside columns, The second layer is fabricated with a sample channel and a carrier gas inlet, which splits into an analytical channel and a reference gas channel, and t valve seats. The analytical gas channel and reference gas channel are much narrower than sample channel such that a proper pressure difference is generated between opposing sides of the diaphragm of injection valve upon introduction of pressurizing gas. The third layer is a flexible diaphragm for valve actuation. The fourth layer is fabricated with a pressurizing gas inlet hole and pressurizing channel leading to the diaphragms of valve seats. The fifth layer serves as another cover plate and a port is etched for connection to the pressurizing tube and carrier gas tank. An external solenoid valve is used to control the processes of sampling and injection. At the normal situation without actuating the solenoid valve, inlet valve and outlet valve are open but injection valve is closed. Sample is drawn into the sample channel by a pump. When the solenoid valve is actuated and gate open, channels are pressurized which leads to closing of inlet/outlet valves and opening of the injection valve so that a plug of sample is injected to the mixing channel and led to the analytical column. Amount of sample injection is controlled by the duration of solenoid valve opening, usually less than 1 second. The channels and valve seats on each layer plate can be fabricated through several well-developed fabrication techniques such as photolithographic, LIGA processes or precision micro machining. All five layers are property aligned and bonded by adhesives. This assembly forms a sound and workable sample injection device.